[PATCH] mm/swap: fix swap cache memcg accounting

[Alexandre Ghiti <alex@ghiti.fr>]

The swap readahead path was recently refactored and while doing this,
the order between the charging of the folio in the memcg and the addition
of the folio in the swap cache was inverted.

Since the accounting of the folio is done while adding the folio to the
swap cache and the folio is not charged in the memcg yet, the accounting
is then done at the node level, which is wrong.

Fix this by charging the folio in the memcg before adding it to the swap cache.

Fixes: 2732acda82c9 ("mm, swap: use swap cache as the swap in synchronize layer")
Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
---
 mm/swap_state.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 6d0eef7470be..48aff2c917c0 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -494,6 +494,10 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry,
 
 	__folio_set_locked(folio);
 	__folio_set_swapbacked(folio);
+
+	if (!charged && mem_cgroup_swapin_charge_folio(folio, NULL, gfp, entry))
+		goto failed;
+
 	for (;;) {
 		ret = swap_cache_add_folio(folio, entry, &shadow);
 		if (!ret)
@@ -514,11 +518,6 @@ static struct folio *__swap_cache_prepare_and_add(swp_entry_t entry,
 			goto failed;
 	}
 
-	if (!charged && mem_cgroup_swapin_charge_folio(folio, NULL, gfp, entry)) {
-		swap_cache_del_folio(folio);
-		goto failed;
-	}
-
 	memcg1_swapin(entry, folio_nr_pages(folio));
 	if (shadow)
 		workingset_refault(folio, shadow);
-- 
2.53.0